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Local anesthetic toxicity and lipid rescue...



"A Mixed (long- and Medium-chain) Triglyceride Lipid Emulsion Extracts Local Anesthetic from Human Serum In Vitro More Effectively than a Long-chain Emulsion"

Anesthesiology, February 2012




Researchers in the U.K. analyzed the difference between mixed (medium- and long-chain) and long-chain lipid emulsions, for their ability to extract local anesthetic from serum. They concluded that the type of emulsion may make the reversal more effective.


The authors used human drug-free serum and added bupivacaine, ropivacaine, or mepivacaine each at a concentration of 10 µg/ml, or bupivacaine 100 µg/ml at pH 7.4, and, in another experiment, bupivacaine 10 µg at pH 6.9. 20% Intralipid®, which has long-chain triglycerides, or 20% Lipofundin®, which contains a 50-50% mixture of medium- and long-chain triglycerides, was then added at 1, 2, or 4% of total volume. The mean decrease in serum drug concentration was then calculated.

The authors’ in vitro model showed overall that Lipofundin® was significantly better than Intralipid® in extracting the drugs from serum. The relative degree of extraction was bupivacaine > ropivacaine > mepivacaine. This order is consistent with the relative partition constant of each drug. As higher concentrations of either Intralipid® or Lipofundin® were used, the percent decrease of bupivacaine increased and a greater effect was seen with Lipofundin® at each % of lipid. A larger percent decrease in serum bupivacaine was observed after 100 µg/ml bupivacaine compared to 10 µg/ml for both Intralipid® and Lipofundin®, and Lipofundi®n extracted more bupivacaine than Intralipid® at each concentration of either lipid. The effect of pH on sequestering bupivacaine was not significant.

These findings call into question the current advanced cardiac life support guidelines specifying use of a long-chain triglyceride emulsion for lipid rescue, although further in vivo studies that confirm a significant improvement in resuscitation from local anesthetic toxicity with lipofundin are obviously required before drawing any confident conclusions. Also, Lipofundin® is currently commercially unavailable in the United States. Indeed, though the study was performed in the United States, the Lipofundin emulsion that was used was a gift from the manufacturer B. Braun Melsungen AG (Melsungen, Germany)

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